The structure of the extracellular polysaccharide (EPS) produced by Erwinia chrysanthemi strain RA3W, a mutant strain of E. chrysanthemi RA3, has been determined using low pressure size-exclusion and anion-exchange chromatographies, high pH anion-exchange chromatography, glycosyl linkage analysis, and 1D 1H NMR spectroscopy. The polysaccharide is structurally similar, if not identical, to the family of EPS produced by such as E. chrysanthemi strains Ech9, Ech9Sm6, and SR260. The molecular weight of EPS RA3W by ultracentrifugation (sedimentation equilibrium) and light scattering is compared with those of other E. chrysanthami EPSs, as are the viscometric properties.